Both Pentax W90 and Pentax W80 have 1/2.3-inch sized 12.0 MP resolution sensors so sensor size and resolution is not a differentiator between these two cameras.
Below you can see the W90 and W80 sensor size comparison.
Pentax W90 and Pentax W80 have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the same focal length and aperture.